Study On The Characteristics Of Fluid Flow And Heat Transfer In Pulsating Heat Pipe And Its Application On Waste Heat Recovery Utilization

The pulsating heat pipe is a high-efficiency heat transfer component based on the heat-driven gas-liquid pulsation evaporation?boiling?-condensation phase change heat transfer in the capillary channel.It has the characteristics of simple structure,low cost,long-distance energy transportation and strong gravity adaptability.Therefore,the pulsating heat pipe has broad development potential in the heat dissipation of electronic devices with multiple heat sources,efficient heat transfer under variable gravity loads,and long-distance waste heat recovery and utilization.At present,the complex gas-liquid two-phase flow in the pulsating heat pipe in multi-heat source mode and its internal mechanism have not been fully revealed,especially the influence mechanism of heating mode and tilt angle on the gas-liquid two-phase pulsating flow behavior and heat transfer characteristics is not clear.Moreover,the mechanism of pulsating heat pipe flow and heat transfer under overload remains to be further studied.In addition,the application of pulsating heat pipes to achieve long-distance pumpless transport of heat against gravity is also scarce.To this end,this paper carried out the research on the flow and heat transfer mechanism of pulsating heat pipe in multi-heat source mode,the research on the flow and heat transfer mechanism of pulsating heat pipe under overload and the anti-gravity waste heat recovery of pulsating heat pipe.In order to understand the complex gas-liquid two-phase flow behavior and internal mechanism in the pulsating heat pipe in multi-heat source mode,the plate pulsating heat pipe for multi-heat source heat dissipation is designed and developed.Under different working inclination angles and three kinds of heating modes,gas-liquid two-phase flow behavior in the pulsating heat pipe,as well as heat transfer characteristics,performance differences between the left and right sides is studied,and starting characteristics such as starting power,starting time,and starting temperature of the plate pulsating heat pipe are investigated.The results indicate that in the full heating mode and the left and right side semi-heating modes,with the increase of heat load,the pulsating heat pipes experience static state?S?,intermittent pulsation?S&P?,and pulsation accompanied by circulation?P&C?and cycle?C?.Among them,the performance of the pulsating heat pipe is optimal in the cyclic operation mode.In the full heating mode,an increase in the heat load and a decrease in the working inclination angle contribute to the generation of the circulation state inside the tube.In the left and right side semi-heating modes,the heat load required for the pulsating heat pipe to enter each working state is not sensitive to the working inclination angle.In the full heating and right heating modes,an increase in the working inclination angle helps the activation of the pulsating heat pipe,while in the left heating mode,the increase in the working inclination angle causes an obstacle to the activation of the pulsating heat pipe.In the three heating modes,the increase of the heat load increases the starting temperature of the pulsating heat pipe,but reduces the starting time of the pulsating heat pipe,and the starting temperature and starting time of the pulsating heat pipe are less sensitive to the working inclination angle.In the full heating mode,the statistic of the degree of data dispersion?the DR value?of the equivalent thermal conductivity between the left and right sides of the pulsating heat pipe increases with the increase of the working inclination angle.The lowest DR value is under the horizontal working inclination angle,and the highest is under the vertical working inclination,the latter is 2.79 times the former.For the left and right side semi-heating modes,the relative change of the DR value of the equivalent thermal conductivity of the left and right sides of the pulsating heat pipe is in the range of 0?to 360?working inclination angle is?37.8%.In the full heating mode,the equivalent thermal conductivity of the pulsating heat pipe is15.8 times that of the6063 aviation aluminum alloy,and its own weight is only 91%of the same volume of6063 aviation aluminum alloy.The relative change in the equivalent thermal conductivity of pulsating heat pipe in the working angle range of 0?to 360?working inclination angle is?16%.In order to study the flow and heat transfer mechanism of the pulsating heat pipe under overload,a rotating platform was designed and built,and the required load was simulated on the ground with the centrifugal acceleration generated by it.The gas-liquid two-phase motion behavior and heat transfer characteristics of the pulsating heat pipe under different loads with two different arrangement modes are studied.The results show that under the circumferential arrangement and the radial arrangement modes,the generation and increase of centrifugal acceleration inhibit the generation of the working fluid circulation in the tube,which leads to the decrease of heat transfer performance.For the circumferential arrangement mode,as the thermal load increases,the working fluid in the tube undergoes the S&P,P&C,and C modes in sequence at 2.5g₀.Among them,the performance of the pulsating heat pipe is optimal in the C mode.At low heat load,the relative change in the equivalent thermal conductivity in the range of 0².5g₀ centrifugal load is?28.2%.At high heat loads,this relative change is reduced to 19.6%due to the increased driving force in the tube.For the radial arrangement mode,as the thermal load increases,the working fluid in the tube undergoes the S&P,P&C and C modes in turn at 2.3g₀.At low heat load,the relative change in equivalent thermal conductivity in the range of 0³.6g₀centrifugal load is?48.6%.At high heat loads,this relative change is reduced to34.8%due to the increased driving force in the tube.In order to study the heat recovery of pulsating heat pipe against gravity,the heat transfer performance of the pulsating heat pipe device is firstly tested.The heat transfer performance and variation of the pulsating heat pipe under three working inclination angles are studied.The experimental platform of the pulsating heat pipe recovering the flue gas residual heat to heat low temperature diesel oil against gravity is designed and developed.The evolution characteristics of the heat-conducting core and fuel under one heating power and different heat transfer schemes are studied.At the same time,the heat recovery performance of waste heat utilization under different working conditions is qualitatively and quantitatively evaluated.The experimental results show that the heat transfer performance of the pulsating heat pipe decreases with the decrease of the working inclination angle.Nevertheless,its equivalent thermal conductivity is still 17.4 times that of pure copper media.In the waste heat recovery,the heat transfer performance of the pulsating heat pipe and the pure copper rod increases with the increase of the heating power,while in this experiment,the equivalent thermal conductivity of the pulsating heat pipe is about 4 times that of the pure copper rod.In addition,the metal grating has a uniform temperature effect in the horizontal direction.In the vertical direction,due to the large temperature gradient,the uniform temperature effect of the metal grating is more obvious.When the pulsating heat pipe is a heat conductive core,the corresponding waste heat recovery efficiency is greatly improved compared to the pure copper rod.The addition of metal gratings also improves the efficiency of waste heat recovery to a certain extent.Compared with the traditional pure copper heat transfer medium used for waste heat recovery,the waste heat recovery efficiency of the waste heat recovery system using the pulsating heat pipe combined with the metal grid can be improved by about 1times,which provides a new idea for recycling waste heat from the top in the actual project.